1. Field of the Invention
The present invention relates to a liquid ejection apparatus, an image forming apparatus, and an ejection determination method, and more particularly to a liquid ejection apparatus, an image forming apparatus, and an ejection determination method that are suitable for detecting ejection errors in an inkjet head in which a plurality of droplet ejection apertures (nozzles) are arranged two-dimensionally.
2. Description of the Related Art
An inkjet recording apparatus forms images on a recording medium by ejecting ink from nozzles while moving a recording head (also called a print head) in which a plurality of nozzles are arranged and a recording medium relatively with respect to each other. In an apparatus of this kind, caused by increase in the viscosity of the ink, infiltration of air bubbles into the ink, or the like, ejection errors may occur, namely, the ink may cease to be ejected from the nozzles, or the amount of the ejected ink (the size of the dot deposited on the recording medium) and the flight direction of the ejected ink (the position of the dot deposited on the recording medium) may become defective.
In view of these problems, a method is known for determining loss of ink or ejection errors by irradiating light, such as laser light, onto droplets of the ink ejected from a recording head to determine variations in the amount of the light obstructed by the droplets (see Japanese Patent Application Publication Nos. 2003-191453 and 2002-361863).
In Japanese Patent Application Publication No. 2003-191453, since the ejection timing of a nozzle group with respect to the ejection of other nozzle groups is staggered within the range the ejection cycle, then positional adjustment between the optical axis and the nozzles is simplified, thereby improving the determination speed.
On the other hand, in Japanese Patent Application Publication No. 2002-361863, bending of the tail of the droplet (bending of the flight direction) is evaluated by determining the timing and duration at which droplets pass through a light beam of a laser detector, or by examining one nozzle from a plurality of directions by means of a plurality of laser determination systems. When a tail bending is detected, the tail bending is corrected by changing the drive waveform.
However, in the technology disclosed in Japanese Patent Application Publication No. 2003-191453, the timings at which droplets are placed in a determination light beam are controlled by time division, and it is impossible to place a plurality of droplets in the light beam simultaneously. It is hence necessary to perform ejection from a plurality of nozzles at timings staggered from each other, and it then needs a long duration to complete the determination of the ejected droplets in respect of all of the nozzles.
Furthermore, in the technology disclosed in Japanese Patent Application Publication No. 2002-361863, the determination is performed by focusing on the passage duration of a droplet passing through a determination light beam, and the determination is only possible if the amount of bending of the flight direction is relatively large. In other words, although it is possible to detect the tail bending which indicates an extreme directional abnormality with respect to normal ejection, it is considered difficult to determine cases where the amount of bending is small, and hence determination accuracy is not good.